First i had the 3d acceleration issue, but thanks to this thread i solved it.

Teh problem now is that everytime i switch back to the game (from the menu, after a load,...) i experience some seconds of lag and stuttering (which can be quite annoying if there is an enemy trying to shoot you down), after that it works nicely.
No such problem without 3d acceleration.

It seems to me as the GPU is caching the level and slows down... but its just an idea.